Juno will study chameleon neutrinos

Last week in China was launched Juno, an international experiment that
aims to reveal once and for all the mysteries of neutrinos, together with two
other future experiments planned worldwide, Hyper-Kamiokande in Japan and LBNF at FERMILAB, and Italy could not
miss. Hundreds of scientists from around the world gathered in these days at
the Institute of High Energy Physics (IHEP) in Beijing, in order to give birth
to an international collaboration for the construction of a gigantic
underground neutrino detector with liquid scintillator, which exploits a
technology that is similar to that used by the experiment Borexino at Gran Sasso National Laboratories. We have talked with
Gioacchino Ranucci of INFN, deputy coordinator of the collaboration. JUNO's
collaboration, in addition to China and Italy, also includes Czech Republic,
France, Finland, Germany, Russia and the United States.

"Juno's goal is to study the
properties of neutrinos, that transform themselves into one another, which
makes them like chameleons" said Ranucci. Today, we have three families of
neutrinos, electron neutrinos, muon neutrinos and tau neutrinos, and what we
observe is the transformation of one into the other, which is called
"property of oscillation." Certainly, this property is adjusted by a
matrix, the mixing matrix, which gives the parameters expressed in trigonometric
form, for instance as angles that, together with the mass differences between
each couple of neutrino types, determine the probability of transformation of a
neutrino from a family to another. It is therefore precisely the properties we
want to investigate."

Specifically, Juno investigates a
particular parameter: the so-called "hierarchy of neutrino mass", which
is the order in which are arranged the masses of the three types of neutrinos.
In other words, scientists want to understand which of the three families of
neutrinos is lighter. To do so, however, they need to take very precise and
very numerous measures that will allow them to properly investigate the
features of this order. For this reason, they need a very sophisticated
equipment, such as Juno. Its technology is actually not very different from
that of another Italian experiment, Borexino, in which researchers are working
in Gran Sasso Laboratories; the difference is the size of the experimental
apparatus.

Juno is a large sphere 35 meters in
diameter, filled with a glittering substance, a hydrocarbon, which sparkles
with elementary particles. So far, nothing different from Borexino. The Juno sphere,
however, contains about 20,000 tons of liquid scintillator, compared to the
less than 1,000 of the experiment at Gran Sasso Laboratories. To avoid the
problem of noise signals, the sphere is immersed in a large pool of water that
acts as a shield for the ambient radioactivity. Both the sphere and the pool
are placed 700 meters deep underground, in order to ensure some protection
against the cosmic rays. Juno will accomplish its scientific task by capturing
and studying the neutrinos copiously coming from a nearby nuclear reactor complex,
at 52 km from the detector. The scintillation light is captured by
photomultipliers and convert it into electrical signals, which are then
analyzed by researchers to decipher the characteristics of neutrinos.

"We are just at the beginning
of the experiment, but we can say that Juno's mission is very ambitious and
hopeful” Ranucci said. "We believe that this experiment, together with
others in the world as Hyper-Kamiokande and LNB, will be a first observation
viewpoint to catch aspects still obscure of our universe, and that, by
unlocking some of the mysteries associated with neutrinos masses, in the future
could open up new energy scales, larger than those are accessible nowadays with
our accelerators.”